Data retrieval devices retrieve bits of data that have been stored on a recordable medium by passing a read head over the medium. Typically, the read head detects a physical property of a portion of the media such as the direction of a magnetic domain or the optical reflectance of the media in order to detect the data stored on the media. The detection of this property results in a read signal.
In order for a retrieval device to operate properly, it is critical that the read head generate a read signal within an acceptable amplitude range. In order to determine if a head will produce an acceptable signal, it is common to measure the head's track average amplitude (TAA), which refers to the average peak-to-peak amplitude of the pulses produced by the read head from a pattern on the media. The optimal value of this measurement depends on the density of the pattern and the sensitivity of the read-channel. If the TAA is too high, the read head may saturate, which distorts the waveforms in the read signal. If the TAA is too low, the signal-to-noise ratio in the read signal will be too low, causing random bit errors.
In the prior art, in order to avoid placing low performing read heads into a device, it has been common to test the read heads before they are assembled into the device. This typically involves connecting test equipment to the output conductors of the heads and measuring the signals generated by the heads. Although such testing removes heads that fail the test, it has been recognized that some heads can pass this screening test yet still perform poorly when integrated into the retrieval device. To address this problem, the prior art has repeated the track average amplitude testing after the heads have been integrated into the retrieval device. This typically involves connecting probes of an external testing system to the output conductors of a common preamplifier in the retrieval device that is connected to each of the heads.
Such testing is undesirable because it requires external test equipment and because it requires a significant amount of time to connect the test equipment to the lines containing the read signal. Thus, a system is needed that allows for testing of the head without requiring external test equipment and without requiring that probes be connected to conductors exiting the device's preamplifier.
Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.